The core vaccines that ALL horses in the US should have (according to the American Association of Equine Practitioners) are: Eastern and Western Equine Encephalitis, Tetanus, Rabies and West Nile Virus. EEE, WEE and WNV area seen in all parts of the US and are transmitted by biting insects, so there is no contact with other horses necessary for these diseases to spread. These diseases all affect the brain and can lead to lack of control over balance and movement which make horses dangerous to themselves and handlers. EEE has a very high mortality rate. WEE and WNV have lower mortality rates strictly from the disease but because supportive care of a horse that cannot stand is expensive and hard to provide they often get euthanized. Tetanus is caused by a bacteria that horses are EXTREMELY susceptible to and that they shed in their feces. When this bacteria gets into a wound it begins to reproduce and in doing so produces toxins. By the time the number of toxins are high enough to show outward symptoms, the infection is well-progressed and the chance of successful treatment is low. So horses live in high risk situations and this is a deadly disease. Rabies--another deadly disease with a high mortality rate. But with this one besides the fact that a horse that contracts the disease is likely to die, they also tend to expose MULTIPLE humans before they are diagnosed with rabies. (Happens every year.)
Besides those core vaccines, there are several risk-based vaccines that should be given based upon the way a horse is kept, it's use, it's age, etc. The most commonly given risk-based vaccines are Influenza and Equine Herpes Virus, both of which are extremely contageous and a serious risk for any horses who show, trail ride, or live in stabling situations with horses who do any of those sorts of things.
Because there is no "one-size-fits-all" vaccination program for horses, it's important to always discuss your horse's situation with your vet to plan an appropriate vaccination program for your horse.
Licensed Veterinary Technician